CWA 16975:2015

SLOVENSKI STANDARD
SIST CWA 16975:2017
01-november-2017
(NRXþLQNRYLWHSRVWDMH]DGDOMLQVNRRJUHYDQMH
Eco-efficient Substations for District Heating
Öko-effiziente Unterstationen
Ta slovenski standard je istoveten z: CWA 16975:2015
ICS:
27.010 Prenos energije in toplote na Energy and heat transfer
splošno engineering in general
91.140.10 Sistemi centralnega Central heating systems
ogrevanja
SIST CWA 16975:2017 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

SIST CWA 16975:2017
SIST CWA 16975:2017
CEN
CWA 16975
WORKSHOP
December 2015
AGREEMENT
ICS 27.010; 91.140.10
English version
Eco-efficient Substations for District Heating
This CEN Workshop Agreement has been drafted and approved by a Workshop of representatives of interested parties, the
constitution of which is indicated in the foreword of this Workshop Agreement.

The formal process followed by the Workshop in the development of this Workshop Agreement has been endorsed by the
National Members of CEN but neither the National Members of CEN nor the CEN-CENELEC Management Centre can be held
accountable for the technical content of this CEN Workshop Agreement or possible conflicts with standards or legislation.

This CEN Workshop Agreement can in no way be held as being an official standard developed by CEN and its Members.

This CEN Workshop Agreement is publicly available as a reference document from the CEN Members National Standard Bodies.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland,
Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta,
Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and United Kingdom.

EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Avenue Marnix 17, B-1000 Brussels
© 2015 CEN All rights of exploitation in any form and by any means reserved worldwide for CEN national Members.

Ref. No.:CWA 16975:2015 E
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Contents
Page
European Foreword .4
1 Scope .5
2 Conformance .5
3 Technical Part.8
3.1 Introduction.8
3.2 Terms and definitions.8
3.3 Eco-efficient substation (EES) definition .10
3.3.1 General.10
3.3.2 Marking of EES.11
3.3.3 Commissioning, service and maintenance of EES.11
3.3.4 Choice of materials .11
3.4 Connection principles and standardized schemes .12
3.4.1 General Scheme of a substation .12
3.4.2 Parallel connection.12
3.4.3 Two step connection .12
3.5 Efficiency of Substation .13
3.5.1 Temperature and pressure levels in DH network.13
3.5.2 Low temperature system .14
3.5.3 Pressure drop .14
3.5.4 Efficiency of heat exchangers .15
3.5.5 Procedure to determine heat exchanger return temperature (T12).15
3.6 Domestic hot water system.16
3.6.1 Functionalities.16
3.6.2 Choice of materials .17
3.6.3 Temperatures, Environmental and Health Requirements for the domestic hot water .17
3.6.4 Dimensioning .17
3.7 Heating systems.17
3.7.1 Dimensioning of Heat Exchangers for heating services.17
3.7.2 Temperature levels for heating systems .18
3.8 Control system and communication.18
3.8.1 General.18
3.8.2 Delivered heat control .18
3.8.3 DHW control system .18
3.8.4 Accuracy of control system .19
3.8.5 Advanced features.19
3.9 Substation components -including heat exchanger, pump, safety equipment, valves .20
3.9.1 Generalities about the components.20
3.9.2 Filter .21
3.9.3 Control valve .21
3.9.4 Piping .21
3.9.5 Sensors.21
3.9.6 Pumps:.22
3.10 Insulation: .22
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4 Environmental Part .22
4.1 Environmental part General .22
4.2 Heat losses in substation.23
4.3 Pressure losses in secondary side heating .24
4.4 Cooling of the return temperature .24
4.4.1 General.24
4.4.2 Demands to Space Heating .25
4.4.3 Demands to DHW.26
4.5 Energy saving functions .27
4.5.1 General.27
4.5.2 Control and limitation of max capacity / primary flow.27
4.5.3 Indoor temperature data .27
4.5.4 Remote monitoring and control .28
4.5.5 Eco function.28
4.6 Labelling system.29
4.6.1 Eco-efficient substation labelling system and summary of rating points in case of
DHW and spice heating side(s).29
4.6.2 Eco-efficient substation labelling system and summary of rating points in case of
only spice heating side(s) .30
5 Testing and certification part.31
5.1 Certification process.31
5.1.1 Introduction.31
5.1.2 Object .31
5.1.3 General rules .31
5.1.4 Administration, Organisation .32
5.1.5 Certification procedure.32
5.1.6 Conditions for certification and quality marking .34
5.2 Testing procedures.37
5.2.1 Assumption and preparations .37
5.2.2 Test methods .44

SIST CWA 16975:2017
European Foreword
CWA 16975 is a technical agreement, developed and approved by an open, independent Workshop
structure within the framework of the CEN-CENELEC system. CWA 16975 reflects the agreement only
of the registered participants responsible for its content, and was developed in accordance with the
CEN-CENELEC rules and practices for the development and approval of CEN/CENELEC Workshop
Agreements. CWA 16975 does not have the status of a European Standard (EN) developed by CEN and
its national Members. It does not represent the wider level of consensus and transparency required for
a European Standard (EN) and is not intended to support legislative requirements or to address issues
with significant health and safety implications. For these reasons, CEN are not accountable for the
technical content of CWA 16975 or for any possible conflicts with national standards or legislation. The
Workshop participants who drafted and approved CWAWS 73 are indicated in the Foreword. The
copyright in CWA VW 73 is owned exclusively by CEN. Copies of CWA VS 73 are available from the
[national standards bodies of the following countries: Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech
Republic, Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece,
Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland,
Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and the United Kingdom.
Foreword
CWA 16975 was developed in accordance with CEN-CENELEC Guide 29 “CEN/CENELEC Workshop
Agreements – The way to rapid agreement” and with the relevant provisions of CEN/CENELEC Internal
Regulations - Part 2. It was agreed on 2015-09-11 in a Workshop by representatives of interested
parties, approved and supported by CEN following a public call for participation made on 2015-09-11. It
does not necessarily reflect the views of all stakeholders that might have an interest in its subject
matter.
The final text of CWA 16975 was submitted to CEN for publication on 2015-11-19. It was developed and
approved by: Paolo Arrus - Giacomini, Anna Boss - SP Swedish National Testing and Research Institut,
Aleš Cjuha - Energetika Ljubljana, Daniele Delboca - Giacomini, Mieczyslaw Dzierzgowski - OPEC
Gdynia, Bertrand Guillemot- Dalkia France, Niklas Jeppsson - SWEP International, Markus Köfinger -
AIT, Alexander Midtsjø - Hafslund Varme, Gunnar Nilsson - Svensk Fjärrvärme, Timo Peltola-Ouman,
Igor Radovic - Grundfos Holding, Fabrice Renaude - Gylergie Cofely's Research Center, Henrik Rietz -
SWEP International, Marko Riipinen - Helsinki Energy, Janusz Rozalski - OPEC Gdynia, Jaroslaw
Szczechowiak - OPEC Gdynia, Jan Eric Thorsen – Danfoss, Jonas Wallenskog - Svensk Fjärrvärme, Wim
Wolfs- Giacomini, Teijo Aaltonen - Alfa Laval Nordic.
It is possible that some elements of CWA 16975 will be subject to patent rights. The CEN-CENELEC
policy on patent rights is set out in CEN-CENELEC Guide 8 “Guidelines for Implementation of the
Common IPR Policy on Patents (and other statutory intellectual property rights based on inventions)”.
CEN shall not be held responsible for identifying any or all such patent rights.
The Workshop participants have made every effort to ensure the reliability and accuracy of the
technical and non-technical content of CWA 16975, but this does not guarantee, either explicitly or
implicitly, its correctness. Users of CWA 16975 should be aware that neither the Workshop participants,
nor CEN can be held liable for damages or losses of any kind whatsoever which may arise from its
application. Users of CWA 16975 do so on their own responsibility and at their own risk.

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1 Scope
The target is to describe what is an eco-efficient substation (EES), how this eco-efficient substation is
considered, tested and certified. EES concept includes as much substation efficient design as possible,
without trying to cover an exhaustive point of view. The scope of the EES is to focus on a reachable
future, realistic compliance with the existing system and ways of handling substation issues in a
harmonized manner across Europe.
The proposed standard is compliable with the expected development in Europe in the future such as:
• New buildings with less demand for energy and more demands for lower temperatures.
• The connection systems should be standardized in order to make the substation replacement
as easy as possible.
The aim is to consider the whole life of the system, including all seasons and not only the peak load
operation. The most important period to consider, is the long duration time with both heating and
domestic hot water demands.
EES should be certified, and marked according to certification that is given according to testing result
and environmental ranking. Only EES with capacity up to 500kW per heat exchanger for heating and
domestic hot water respectively, can be certified. Small substations intended for single-family houses or
flats, shall not be certified. A certificate can include one specific substation or a series of substations.
This document contains 3 main parts:
Technical: Describes the main and optional components of the EES
Environmental: Describes the various parameter and components that give the efficiency to the
substation, how these are ranked and the marking procedure
Testing and certification: The testing and certification procedures.
2 Conformance
All DH equipment and the system as a whole shall be approved in accordance with international,
European Union and national laws, regulations, building codes and standards. In addition, all laws and
rules from the national health and environmental authorities shall be taken into consideration.
National DH organizations and Euroheat & Power should make efforts towards harmonizing such rules
and standards throughout the EU, in order for these rules and standards to be as much as possible in
line with the characteristics of DH. The aforementioned organizations may also issue technical
recommendations themselves.
The following EU directives and standards are relevant for this document:
• Directive 2012/27/EU (EED directive): Energy efficiency directive introduces a framework of
measures to use energy more efficiently at all stages of energy chain. The directive is especially
focused on energy efficiency improvements in households, industry and transport sector.
• Directive 2010/31/EU (EPBD directive): Energy performance of buildings directive introduces
the new methodology for calculating the energy efficiency of buildings, minimum requirements
for energy efficiency of new and renovated buildings, minimum requirements for energy
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efficiency of building equipment, plans for implementing more nearly zero energy buildings,
regular inspections of heating and air conditioning systems in buildings and implementation of
energy performance certificates for buildings.
• Directive 2010/30/EU: Directive establishes a framework for labelling and introducing
general product information on consumption of energy and other energy-related products.
• Directive 2009/125/EC: Directive represents a framework for minimum Eco design
requirements of product that use energy and water (light bulbs, refrigerators, heat Owen,
insulation materials, etc.).
• Regulation No. 641/2009 with amending regulation No. 622/2012 and regulation No.
547/2012: Regulations present eco-design requirements for water pumps.
• Directive 2004/22/EC (MID directive): Measuring instrument directive specifies
methodology and requirements for measuring instruments such as heat, water, gas and electric
energy meters, exhaust gas analysers, taximeters, etc.
• Directive 98/83/EC (DWD directive): Drinking water directive sets the minimum standards for
quality of drinking water in distribution systems, regarding microorganisms and chemical
parameters.
• Directive 97/23/EC (PED directive): Pressure equipment directive presents requirements for
design and fabrication of pressure equipment such as pressure vessels, piping, safety valves and
other components subjected to pressure load.
• Regulation EC 66/2010 (ECO labelling): Regulation presents rules for application of voluntary
environmental labelling system for eco-friendly products.
• European standard EN 1434 (Heat meters standard): Standard specifies minimum
requirements for heat meters regarding construction, data exchange, testing, verification,
installation, commissioning, monitoring and maintenance.
• European standard EN 13445 (Pressure vessels standard): Standard specifies requirements for
design, construction, inspection and testing of unfired pressure vessels made from steel, cast
iron and aluminium.
• European standard EN 1148:1998, EN 1148:1998/A1:2005 (Heat exchangers standard):
Standard specifies test procedures for establishing the performance data of water to water heat
exchangers for district heating.
• European standard EN 247:1997 (Heat exchangers standard): Standard specifies heat
exchangers terminology.
• European standard EN 12828:2012 (Heating systems in buildings standard): Standard specifies
the design of water based heating systems.
• European standard EN 14336:2004 (Heating systems in buildings standard): Standard specifies
the installation and commissioning of water based heating systems.
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• European standard EN 15316 series (Heating systems in buildings standard): Standard
specifies methods for calculation of system energy requirements and system efficiencies; with
special focus on Part 4-5 'Space heating generation systems, the performance and quality of
district heating and large volume systems.
All electrical components of the EES shall be electrically protected according to the applicable rules.
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3 Technical Part
3.1 Introduction
The aim of this part is to describe the technical specifications that a substation has to fulfil to be
regarded as an Eco-efficient substation.
3.2 Terms and definitions
Here is a simplified drawing of a substation that gives the location of the various components described
in the definition.
District Heating
Customer side
T T
11 42
DH supply
DHW supply T° DHW
T° supply
∆P
T DHW
T
41 T
Pressure Supply PS 61
DHW Circulation (T° C)
T
Cold water (T° CW)
∆P
DH
SUBSTATION
T22
Heating supply
DH return T° HS
∆P
Heating
T
12 T
T° return
PR Pressure return Heating return
T
T° HR
Figure 1 - Definition drawing
DHW: Domestic Hot Water: Water heated for sanitary use.
DHW circulation loop: Piping where DHW continuously flows in order to keep the system active and the
temperature on such a level that both comfort and health requirements are delivered to the customer.
Cold Water: Is the fresh water coming from the water services that feed the DHW system.
DH: District Heating Network.
ΔP: Pressure difference between supply and return pipes.

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Definition of variables in a counter-flow heat exchanger
T Primary supply temperature from DH,
11 :
T Heating supply temperature, to customer,
22:
T Primary return temperature to DH,
12:
T21: Heating return temperature, from customer,
T DHW: Primary supply temperature from DH,
31:
T DHW supply temperature to customer,
42:
T DHW Primary return temperature to DH,
32:
Figure 2 - Variables in a heating counter-flow
heat exchanger
T DHW cold water and circulation loop temperature,
41:
ΔΤ2 Temperature difference secondary side,
T51: Cold Water temperature,
T61: Circulation loop return temperature,
ϑ Temperature difference heating (T12–T21) or DHW
side (T32– T41),
ϑ2 Temperature difference Primary side (T11–T22) or (T31–
T ).
Figure 3 - Variables in a DHW counter-flow heat

exchanger
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In this document, the following verbal forms are used:
• “Shall” indicates a requirement
• “Should” indicates a recommendation;
• “May” indicates a permission;
• “Can” indicates a possibility or a capability.
3.3 Eco-efficient substation (EES) definition
3.3.1 General
The purpose of this document is to describe what an Eco-efficient substation is. The substation is the
system in a district heating network, that connects the customer or group of customers to the network.
It complies with European and local regulations. Many various system designs are existing and this
document will describe those that provide the best ratio between energy efficiency, life cycle cost, the
most common use and new services that the substation might provide.
The EES provides both heat service (HS) and domestic hot water production (DHW) or the systems
might be considered separately if just one of the two is needed. It is suitable to consider Rehva request
and/or bacteriological risks according to national regulations when DHW is planned and installed.
To be efficient the Eco-efficient Substation (EES) shall deliver a reasonably low return temperature to
the network and create a reasonably low pressure drop across the system on the secondary side.
The EES shall be equipped to provide the customer and the district heating company with a secure,
energy effective and economically reliable connection to the DH-network. To achieve this target, the
EES shall include at least:
• One efficient heat exchanger per service such as brazed heat exchanger or any other
technology that provide the similar efficient service.
• Each heat exchanger shall be insulated.
• Control valve to control the energy delivered and control the temperature delivered to the
customer in an as efficient manner as possible. A control valve for temperature control
acts on the primary side for each service, heating and DHW.
• Filter should be installed on primary side
• Heat meter should be mounted according to EN 1434.
The number, quality and range of the devices shall be adjusted to the size of the substation. EES shall be
insulated to prevent heat losses, risk of injury and high ambient temperature in the substation room.
Other components can increase the scope of the services of the EES, but as they are strongly linked to
where they have to be implemented in the sizing and design, they are not in the scope of this document.
These components are for example: Storage or any tank, circulation pumps, pressurization devices,
water treatment devices, secondary side filter and other possible components.
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3.3.2 Marking of EES
Substations shall have a permanent and visible attached plate containing the following information:
• Manufacturer; Article No.; Type; Manufacturing No.; Manufacturing year;
• Design temperature; Design pressure; Leakage test pressure; Volume per side; Safety
valves settings (when fitted);
• Heating capacity and DHW capacity; Temperature program for heating, DHW; Voltage;
• Fluid group; Directive 97/23/EC - PED Category or article 3.3;
• EES certification level.
3.3.3 Commissioning, service and maintenance of EES
Customer satisfaction is essential for maintaining and increasing the market position of DH.
Guaranteeing a smooth and economic operation of the district heating supply requires commissioning,
regular inspection and maintenance of the substations and their components. Although the substations
are extremely reliable and have a long lifetime, it is recommended for a specialist to make
commissioning at the first installation and regular inspections to verify that the operation is optimized.
Apart from smaller maintenance work, looming malfunctions will be recognized and eliminated at an
early stage. Valid technical regulations contain only a recommendation to carry out technical
inspections; specified periods are not prescribed, monitoring and surveillance can give indication when
needed.
3.3.4 Choice of materials
To ensure a high quality service, there are a number of criteria that all used materials shall fulfil:
• They shall be selected in order for them to withstand the maximum pressure that the
system is designed for. The materials shall also withstand the maximum temperature that
the system is designed for.
• If there is a mix of materials they shall be chosen in such a way, that corrosion shall be
minimized when considering the whole circuit they will be connected to;
• Water is the most common existing solvent and can in some cases be very aggressive.
When choosing materials for a domestic hot water system, attention shall be paid to the
quality and chemical composition of the local water source to avoid corrosion in the
system;
• Both metals and polymers are used in the circuits. For example in gaskets. The same care
has to be taken in choosing gaskets for the system. They shall withstand the working
conditions in the system for the period that the system is designed for.
The choice of material shall also follow national requirements and regulations.
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3.4 Connection principles and standardized schemes
3.4.1 General Scheme of a substation
According to the services, the EES has to provide various arrangements of the heat exchanger.
The following schemes present connection principles and content of substations. All needed and
obligatory components are presented in these schemes.
The Heating system can include more circuits and heat exchangers, depending on the service the EES
has to provide. Drawings below describe the simplest arrangement.
3.4.2 Parallel connection
The district heating water flows from space heat exchanger directly back to district heating system.
DHW heat exchanger does not utilize return water from space heating side to preheat the DHW.
In parallel connection, there is no extra pressure losses for the DHW heat exchanger.

Figure 4 — Parallel connected EES substation
3.4.3 Two step connection
The district heating water flows from space heat exchanger through the pre-heater of DHW and
improves the total cooling of the district heating system. The influence depends on consumption of
DHW and return temperature from space heating. The two-step EES includes two parts: pre-heater and
post-heater.
Pressure loss on the primary side can become high, if the flow from the space heating side is bigger than
the dimensioned flow through the DHW heat exchanger. In this case, the pre-heater can have problems
in managing the whole flow passing through the heat exchanger.
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Figure 5 — 2-step connected EES substation
3.5 Efficiency of Substation
3.5.1 Temperature and pressure levels in DH network
Temperature on primary side of every substation changes, depending on the district
heating organization, the season, the outdoor temperature and the location of the
substation in the network. Temperature on the secondary side of the substation depends
on the services to be provided, the internal building system to be served, the season and
the outdoor temperature.
The district heating supplier shall provide information that is useful for the design.
Present and future operating data of the location of the substation at the service
connection valves should be provided as:
• Supply pressure,
• Minimum and maximum differential pressure.

The building owner shall provide the customer’s side parameters as:
• Minimum and maximum differential pressure on the secondary side and
temperatures on both sides of the substation. This data should be used for
determining the necessary sizes and capacities of control valves and heat
exchangers, and all other substation equipment.

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3.5.2 Low temperature system
The general tendency of district heating is to increase efficiency in order to achieve decreased
environmental impact and possibilities to improve both cost levels and environmental efficiency during
the whole life time duration. Then the global efficiency could be increased with higher waste heat
recovery, higher cogeneration efficiency, more use of renewables as well as the heat losses decrease
and cheaper equipment is possible to use.
The lower limit for low temperature systems should be set by the need for domestic hot water. Even if
no harmonized European rules exist, the system temperature shall be able to provide the locally
requested temperatures. The lowest temperature that exists in many countries is 50 °C at the tap in a
building. To be sure, to provide this requested temperature at the tap, the loop temperature has to be
slightly higher or up to 60°C, as recommended by the REHVA guidebook. 60 °C is common in DHW
circulation loops in some countries to prevent health problems although 50 °C is sufficient in other
countries.
Then the range of 55-70 °C as a primary supply temperature shall comply with all health requirements
from all European nations’ health authorities.
Most of the conventional techniques are able to provide the expected comfort temperature (around
21 °C in several countries) with a supply temperature around 60°C. Exceptions exist for some hospitals
and others but that cannot be the main argument for higher temperature levels in the whole system.
Such specific demands have to be solved locally for that customer.
The primary supply design temperature at about 60°C allows:
• To supply both domestic hot water and heat with a single pipe system.
• Comply with all health requirements in almost all European countries.
• To use other materials than steel for the pipes.
• To continue to operate the substation and the whole DH system at a slightly higher
temperature when the district heating network needs supply peak capacities.

If the supply temperature in summer is above 70 °C it is not to be regarded as low temperature systems
anymore.
The heat exchanger should be designed and sized for this low temperature level. For the same DHW
demand the heat exchanger will be bigger compared to those sized for 110, 100 or 80°C or what is used
as the supply temperature today. In principal, this is handled in the chapter 3.5.4.

3.5.3 Pressure drop
The district heating parameters supplied by the DH operator shall provide information on the actual
minimum and maximum differential pressures, and maximum pressure measured at the service
connection valves. This data shall be used for determining the ESS components. The total pressure drop
that is needed in the substation shall cover pressure drop for all various components.
The pressure drop at full flow on secondary side of EES should be limited to 15 kPa for the heat
exchanger.
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For domestic hot water, the pressure drop at full flow on secondary side of EES should be
limited to 40 kPa for the heat exchanger.

3.5.4 Efficiency of heat exchangers
The heat exchangers applied in eco-efficient substations shall have adequate heat transfer, securing
high level of energy efficiency at a reasonable cost level.
Based on this demand, the dimensioning temperatures are specified for relevant operating temperature
ranges for space heating and DHW. The relevant variables to consider are presented in figure 1.

3.5.5 Procedure to determine heat exchanger return temperature (T12)
The procedure to determine the maximum DH return temperature (T ) for the example of heating is
explained by the example below.

DH supply temperature, T = 100°C
Heating output temperature, T = 60°C
Heating return temperature, T21 = 40°C
These values are needed input values.
T can be determined by the following steps:
= T – T = 100 – 60 = 40°C.
1. Calculate ϑ 11 22
2. Calculate ΔT = T – T = 60 – 40 = 20°C.
2 22 21
3. Obtain ϑ from table 1 (for space heating), where the calculated values for ΔT and ϑ are used to find
1 2
the corresponding ϑ value. The value of ϑ = 3.0°C for this example.
1 1
4. The maximum DH return temperature, T , is calculated by T = T + ϑ = 43.0°C.
12 12 21
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Table 1 — Space Heating
Space Heating ΔT
ϑ2 ΔT = < 20 ΔT = 21-30 ΔT = 31-45
2 2 2
>=40 3,0 3,0 3,0
35-39 3,0 3,0 3,5
30-34 3,0 3,0 4,0
25-29 3,5 3,5 5,0
20-24 4,0 4,0 6,0
15-19 5,0 5,5 6,5
10-14 5,5 6,5 10,0
5-9 6,5 9,5 13,0
For space heating; ϑ values can be obtained based on given ϑ and ΔT . All figures in °C.
1 2 2
Similar principle shall be applied for the case of DHW, but then Table 2 is used instead.

Table 2 — Domestic Hot Water
DHW
ΔT
ΔT =< 35 ΔT =36-40 ΔT =41-45 ΔT =46-50 ΔT =51-60
ϑ2
2 2 2 2 2
>=40 3,0 3,5
35-39 3,5 4,0 4,5
30-34 4,5 5,0 5,0 6,0
25-29 5,5 6,0 6,5 7,5 10,0
20-24 7,0 7,5 8,0 8,5 10,5
15-19 9,0 9,5 10,0 10,5 11,5
10-14 9,5 10,5 12,0 13,0 14,0
5-9 11,0 13,0 14,5 16,0 18,0
For DHW; ϑ values can be obtained based on given ϑ and ΔT . All figures in °C.
1 2 2
3.6 Domestic hot water system
3.6.1 Functionalities
This chapter describes the functionalities that the eco-efficient substation should fulfil. It is possible to
add more functions and components to substations if the customer desires, or if special conditions are
present. The functionalities are designed to ensure the most preferable means to produce DHW
complying with all the applicable regulations and provide a good cooling of district heating water. If
better solutions are found from the cooling point of view, it is recommended to use those.
The recommended positions of components within the substation can be modified for construction
reasons.
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3.6.2 Choice of materials
According to requirement of chapter 3.3.3, to ensure a safe and healthy production of the domestic hot
water, other criteria shall be fulfilled:
- The materials in question should not release harmful or poisonous substances into the water;
- The materials in question should not contribute to the development of bacteria.
It is not only metals that are used in domestic hot water systems, but also polymers, in gaskets, for
example. The same care has to be taken in choosing gaskets for the system; one should ensure that they
can withstand the working conditions in the system for the period the system is designed for and that
they neither add harmful or poisonous substances to the water nor contribute to the development of
bacteria in the water.
The choice of material shall also follow national requirements and regulations.

3.6.3 Temperatures, Environmental and Health Requirements for the domestic hot water
In order to achieve national temperature requirements for the domestic hot water system one shall be
able to control temperature level of the DHW flow. These parameters should be recorded.
Bacteria and Legionella are not problems specific to district heating. They occur in all hot water systems
(heating oil/natural gas/solar/electric). The contamination of the system especially with Legionella
takes place:
- In the domestic plant, i.e. in the drinking water pipe system, the circulation and the storage tank.
The owner of the secondary hot water system is responsible for its good functioning.
- The heat substation should enable production of the sufficient quantities of hot water in order to
perform the disinfection of bacteria according to local regulations.

3.6.4 Dimensioning
Regardless of the type and the material of the heat exchanger, the basic objective is that heat
exchangers are to be dimensioned and built in a way that they provide the customer with sufficient hot
water in all normal circumstances. Dimensioning should be done in summer rather than winter
conditions in the district heating network so that the hardest constrains are taken into consideration.
The cooling of the DH return shall be as effective as possible in all conditions and all water flows should
run along the heat exchanger surfaces.

3.7 Heating systems
3.7.1 Dimensioning of Heat Exchangers for heating services
Heating systems shall be dimensioned according to customer needs and present and future DH
parameters. The trend to reduce District Heating (DH) supplied temperature should be taken into
account when sizing the system. The DH should have summer temperature above 55°C and winter not
above 110°C. Customer has to fix the capacity and secondary side parameters so that good indoor
quality can be reached in every normal circumstance. In most cases, the design outdoor temperature
SIST CWA 16975:2017
determines the heat exchanger capacity for heating systems. However, in some cases, there may be a
special operating mode, which determines the maximum capacity of the heat exchanger at some other
outdoor temperature. When needed, calculations should also be made to ensure that part load ca
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